 Dear students, in this topic we shall discuss thermoreception. Thermoreception is the sense by which an organism perceives hot or cold temperatures. Thermoreception takes place with the help of thermoreceptors. Thermoreceptors are located in the skin on the upper surface of the tongue and they are also present in the anterior hypothalamus. The skin thermoreceptors detect changes in environmental temperature while the thermoreceptors present in the anterior hypothalamus detect changes in the body's core temperature. The thermoreceptors are a phasic type of receptors. These phasic type of receptors are highly sensitive and they respond rapidly to minute changes in temperature. However, these types of receptors adapt very quickly and quit responding. If the stimulus persists, it will immediately respond but then it will adapt and then it will not generate impulses. These receptors are called phasic receptors and we know that thermoreceptors are phasic receptors. There are two types of thermoreceptors which are present in the external skin and upper surface of tongue. These two types are the cold receptors and warm receptors or warmth receptors. Both these types of receptors are quite sensitive and enable the humans to detect temperatures with too much accuracy that their limit can be as low as 0.01 degree centigrade variation. We shall discuss these two types of receptors in detail. The cold receptors are 3.5 times more in the skin as compared to the warmth receptors. These receptors consist of free nerve endings of neurons which have thin and myelinated A-segma fibers. These fibers have faster conduction speed of about 19 meter per second. They increase their firing rate when skin is cooled below body temperature. The warmth receptors also consist of free nerve endings but their neurons have unmyelinated C fibers. These fibers have low conduction speed of about 0.8 meter per second. These receptors increase their firing rate when the external temperature rises more than the body temperature. In both types of thermoreceptors, specialized receptor proteins are present. These proteins are present in the membranes of thermoreceptors and they belong to a family of ion channel proteins which are called TRP proteins that is Transient Receptor Potential Proteins. This TRP family of receptors is a very big family and it has many sub-families. Our sub-family is involved in different types of receptors. The TRPs involved in thermoreception are of three types TRP A, M and V. Out of these, TRP A and M are involved in the transduction of temperature in cold receptors while TRP M is involved in warmth reception. These TRP ion channel proteins allow, when they are activated, they allow influx of many cations, but especially the calcium ions. The increased ionic concentration depolarizes the membrane and causes the action potentials to be generated. These students, the neural pathways of temperature sensation for both warm and cool sensation, transduce information along the same neural pathways. The cell bodies of the neurons of the thermoreceptors which are present in the skin behind these nerve endings and the cell bodies, those cell bodies reside in the dorsal root ganglion DRG and trigeminal ganglion on the dorsal horn of spinal cart. The cell bodies are present in the DRG and the dorsal horn of the spinal cart. This is how these neurons have long axons and their axons are in the skin but their cell bodies are present in the DRG and the dorsal horn of the spinal cart. Now, the pathway of this nerve impulse is that the neurons of the dorsal horn communicate through synapses with the brain's thalamus. From there, the neurons communicate with the hypothalamus. Similarly, from the skin to the spinal cart, from the spinal cart to the thalamus and from the thalamus to the hypothalamus, this is the perception of heat or cold. And finally, the hypothalamus is the part which elicits a proper thermoregulatory response.